1. Field of the Invention
The present invention relates to an endoscope whose contents will resist high-temperature high-pressure steam given off during autoclaving so as not to be destroyed or deteriorated, and whose insertion unit has a soft part.
2. Description of the Related Art
Endoscopes having an insertion unit thereof inserted into a body cavity for observation of a deep region or for medical treatments to be, if necessary, conducted using a treatment appliance have been widely used in the field of medicine.
In the case of endoscopes for medical studies, disinfecting and sterilizing a used endoscope is essential for preventing infectious diseases. A sterilization gas such as an ethylene oxide (EOG) gas or a disinfectant has been used to disinfect and sterilize a used endoscope in the past.
However, sterilization gases are, as already known, quite toxic. Sterilization work cannot help becoming imperfect because it must be carried out safely. Moreover, adverse effects of a sterilization gas on an environment are in question. Since it takes much time for aeration intended to remove gas sticking on equipment after sterilization, a sterilized endoscope cannot be used immediately after sterilization. Moreover, there is a question of a high running cost.
On the other hand, disinfectants are hard to manage. Besides, the fact that a great expense is needed to dispose of a disinfectant must be taken into consideration.
Autoclaving has become a mainstream of disinfection and sterilization of endoscopic equipment these days. This is because autoclaving does not require time-consuming work, makes it possible to use equipment immediately after autoclaving, and costs a little for running.
Typical conditions for autoclaving are stipulated as the ANSI/AAMI ST37-1992 acknowledged by the American National Standards Institute and issued by the Association for the Advancement of Medical Instrumentation. The conditions define that pre-vacuum type autoclaving should be performed at 132° C. for four minutes and that gravity type autoclaving should be performed at 132° C. for ten minutes. Degrees of temperature at which autoclaving is actually performed range from 115° C. to 140° C. in general.
A typical process of pre-vacuum type autoclaving includes a pre-vacuum step, a sterilization step, and a drying step. At the pre-vacuum step, a sterilization chamber in which medical equipment to be sterilized is stowed is decompressed to exhibit a negative pressure. At the sterilization step, high-pressure high-temperature steam is injected into the sterilization chamber for sterilization. At the drying step, the sterilization chamber is decompressed again in order to dry a sterilized endoscope.
The pre-vacuum step is a step intended to facilitate infiltration of steam into the minute spaces in medical equipment which is performed at the sterilization step. The sterilization chamber is decompressed, whereby high-pressure high-temperature steam penetrates the whole of the stowed medical equipment. The pressure in the sterilization chamber to be attained at the pre-vacuum step and drying step is calculated as “an atmospheric pressure −0.07 MPa or so.” The pre-vacuum step is included in a process of gaseous sterilization using an ethylene oxide gas. The pressure to be attained at the sterilization step is often set to a value calculated as “the atmospheric pressure +0.2 MPa or so.”
In general, endoscopes have a soft insertion unit or are of a bendable type having a bendable part. In this case, an armor tube made of a soft polymeric material such as a rubber or elastomer is used as a casing member for the soft insertion unit or bendable part. Moreover, since the endoscopes must be immersed in a fluid agent, the endoscopes are entirely watertight.
When a watertight endoscope is autoclaved, a soft armor tube may dilate to break at the decompression step such as the pre-vacuum step. Otherwise, a joint of parts may not fail to resist a difference in pressure between the interior and exterior of the endoscope any longer, and may eventually be broken.
For preventing the above incident, Japanese Unexamined Utility Model Publication No. 1-12802 has disclosed an interior-exterior communication device for airtight endoscopes.
According to the utility model, when a process of gaseous sterilization including a pre-vacuum step is adopted, an airtightness release cap is attached to the interior-exterior communication device, which is located on the outer wall of an endoscope, at each decompression step. This is intended to allow the internal space of the endoscope (or in other words, the interior of the endoscope) to communicate with the exterior of the endoscope for preventing a burst of a bendable armor tube of a bendable part.
Moreover, Japanese Unexamined Patent Publication No. 63-315024 describes an endoscope structured so that a communication path formed in part of the outer wall of the endoscope is blocked using a waterproof cap. The endoscope is sterilized using a gas with the waterproof cap removed. It is thus prevented that an armor tube of a bendable part or the like bursts at a decompression step.
However, as far as autoclaving is concerned, the interior and exterior of an endoscope are allowed to communicate with each other, and high-pressure high-temperature steam is actively invaded into the interior. This poses a problem in that various contents of the endoscope including an observing means and internal structural members thereof deteriorate shortly because of the steam.
In efforts to cope with the problem, Japanese Examined Patent Publication No. 4-67445 has disclosed an internal pressure adjustment device for airtight endoscopes. The internal pressure adjustment device has a non-return valve mechanism located on a housing of an endoscope. The non-return valve mechanism permits passage of gas from the interior of the endoscope to the exterior thereof but prevents invasion of gas from the exterior of the endoscope into the interior thereof. Even when autoclaving is performed, it is prevented that high-pressure high-temperature steam actively invades into the interior of the endoscope.
However, an endoscope may include members made of a polymeric material such as a plastic or rubber. In this case, when the endoscope is autoclaved, high-pressure high-temperature steam permeates through the polymeric members and invades into the interior of the endoscope. In other words, unless all members constituting an endoscope are made of a raw material such as a metal, ceramic (in a broad sense, including a glass), or crystalline material, and assembled without a gap, high-pressure high-temperature steam will invade into the interior of the endoscope during autoclaving.
The Japanese Examined Patent Publication No. 4-67445 has disclosed an endoscope having a non-return valve mechanism. If the endoscope is an endoscope with a bending ability whose insertion unit has a bendable part, the bendable part is sheathed with an armor tube made of a polymeric material such as a soft rubber or elastomer. High-pressure high-temperature steam permeates through the armor tube and gradually invades into the interior of the endoscope.
Moreover, in the endoscope with a bending ability, a rubber-sealing member made of a polymeric material such as an O ring is used as a sealing member for sealing an axis of rotation of a bending lever used to bend the bendable part. High-pressure high-temperature steam used for autoclaving permeates through the rubber-sealing member and gradually invades into the interior of the endoscope.
Furthermore, even when an insertion unit of an endoscope does not have the bending ability, if the whole insertion unit is soft, a polymeric material is used to make the armor tube of the insertion unit. During autoclaving, high-pressure high-temperature steam permeates through the armor tube and gradually invades into the interior of the endoscope.
Endoscopes referred to as airtight endoscopes include endoscopes having a bending ability and endoscopes each of which insertion unit is soft. In these endoscopes, high-pressure high-temperature steam given off during autoclaving, as mentioned above, permeates through a member made of a polymeric material and gradually invades into the interior of the endoscope.
The phenomenon that steam invades into the interior of an endoscope takes place during autoclaving irrespective of whether the autoclaving is of a pre-vacuum type or gravity type.
When steam invades into the interior of an endoscope, there arises a fear that various contents of the endoscope including an observing means and internal structural members thereof may deteriorate, though gradually.
An electronic endoscope will be taken for instance. Steam invading into the interior of the endoscope may condense on the surface of a lens included in an objective unit incorporated in an imaging unit or the internal surface of a cover glass of the objective unit. Moreover, electronic parts including a solid-state imaging device may malfunction. In either case, there arises a possibility that invading steam impairs the quality of a view.
Moreover, when steam invading into the interior of an endoscope reaches an observation optical system, the steam may condense on the surface of a lens included in the observation optical system or the internal surface of a cover glass of the observation optical system to narrow a field of view. This is not limited to the electronic endoscope, but the same applies to a fiberscope.
Furthermore, a multi-component glass that can be machined readily is a lens glass widely used as the foregoing lens or cover glass. The multi-component glass deteriorates when exposed to high-pressure high-temperature steam given off during autoclaving. When steam invades into the interior of an endoscope, the glass itself may deteriorate or a coating formed on the surface of the lens or an adhesive applied to the surface thereof may deteriorate. This may impair the quality of a view.
Japanese Unexamined Patent Publication No. 62-212614 describes an endoscope in which at least part of an optical system is structured hermetically in order to prevent invasion of steam into the optical system. However, the endoscope has optical members including a lens and cover glass bonded to a frame using an adhesive. When autoclaving is performed under the conditions stipulated by the American National Standards Institute and others, steam invades into the optical system through the adhesive. In short, the structure cannot hinder invasion of high-pressure high-temperature steam in practice.
Under the foregoing conditions for autoclaving, high-pressure high-temperature steam permeates through a layer of a hardened adhesive whose major component is a polymeric material, such as, a generally adopted epoxy adhesive or silicone adhesive.
Moreover, the strength of a joint secured with the above adhesive is not so high as that of a joint secured by performing welding. When parts made of different materials, for example, a metal and glass are joined using an adhesive, the coefficient of thermal expansion differs between the parts. When the parts change due to heat during autoclaving, the joint of the parts is stressed. Consequently, the adhesive may peel off.
In consideration of the foregoing drawbacks, a rigid endoscope having a rigid insertion unit has, as described in Japanese Unexamined Patent Publication No. 9-265046, a cover glass hermetically locked in a sleeve, which is one of parts constituting a housing of the endoscope, without a gap by performing soldering. A housing structure serving as the housing of the endoscope is thus sealed hermetically.
However, in the case of an endoscope whose insertion unit has a bendable part or whose insertion unit is at least partly soft, a member made of a polymeric material is used as at least part of a housing of the endoscope. Even if only the distal part of the insertion unit has members thereof joined hermetically, the whole of the housing of the endoscope cannot be sealed fully hermetically.
In other words, the endoscope whose housing can be sealed hermetically as described in the Japanese Unexamined Patent Publication No. 9-265047 is limited to rigid endoscopes not having the bending ability and making it possible to make an insertion unit thereof using a metal or ceramic.